Corrections 18 March ’08 – I have uploaded a revised chart which now shows the correct hexagonal benzene rings for serotonin and pencillin; thanks to ‘As you lean’ for pointing out the errors in the original

Heterocyclic molecules have atoms other than carbon (hetero-) in a carbon ring structure (-cyclic). The molecules on this hat are …

Thank you thank you!
I’m plotting a pair of organic chemistry socks… and you’ve given me a brilliant and well directed launching point! Mine will be textured, not color work (I only have one skein of multi-colored yarn, and though black would be good… I have none to go with it), but I will almost certainly be using caffeine! Maybe also the chocolate one, and serotonin.
You’ve made my day!
(If only the chemist in question lived on this continent, I’d totally make the hat for him)